Solvent resistant polycarbonate compositions

ABSTRACT

Polymeric compositions are described which result from blending a mixture comprising: (A) at least one amorphous polycarbonate; (B) at least one cyclic polycarbonate oligomer containing hydroquinone carbonate structural units; and (C) at least one polycarbonate formation catalyst. The polymeric compositions have particular application in the preparation of shaped articles for use in environments characterized by the presence of solvents, solvent vapors, and/or potential for fire conditions. Methods for increasing the solvent and flammability resistance of amorphous polycarbonates are also described.

FIELD OF THE INVENTION

This invention relates generally to methods for increasing the solventand flammability resistance of amorphous polycarbonates and to polymericcompositions resultant from blending a mixture comprising an amorphouspolycarbonate resin, a polycarbonate oligomer, and a polycarbonateformation catalyst.

BACKGROUND OF THE INVENTION

Polycarbonates are well-known resins which have good property profiles,particularly with respect to impact resistance, electrical properties,optical clarity, dimensional stability and the like. Polycarbonates areused in applications requiring extreme toughness, transparency,resistance to burning, and maintenance of useful engineering propertiesover a wide temperature range. Typical applications include: bubblehelmets for astronauts, canopies for supersonic aircraft, furnishingsfor commercial aircraft, break-resistant windows, transparentbullet-resistant laminates, impact-resistant lenses, combinationelectrical insulation and mechanical housings for appliances, automotiveinstrument panels, and the like.

One polycarbonate resin that has been used successfully in suchenvironments is based on bisphenol A ("BPA"). The relevant art prior toBPA-polycarbonates and the subsequent development of this material as anengineering resin is reviewed in H. Schnell, Chemistry and Physics ofPolycarbonates, Wiley-Interscience, New York (1964) and K. Johnson,Polycarbonates Recent Developments, Noyes Beta Corp., Parkridge, N.J.(1970).

While BPA-polycarbonate provides significant benefits, this resin andrelated amorphous polycarbonates have certain disadvantages. Mostnotably, the resistance of amorphous polycarbonates to organic solventsis rather limited. The tendency of organic solvents to crystallize,craze, crack or mar the surface of objects made from such polycarbonatesnaturally limits their application. For example, tensile strains mayreadily be "frozen in" to polycarbonate parts during fabrication byinjection molding and, when compounded with stresses encountered inservice, result later in crazing on exposure to unfavorableenvironments. The presence of solvents or solvent vapors in suchenvironments may alter threshold conditions for crazing to the pointwhere parts under mechanical stress will fail. Therefore, environmentalconditions as well as stresses to be encountered in fabrication and inservice must be considered carefully in designing for polycarbonates.

There have been a number of attempts to improve the solvent resistanceof BPA-polycarbonate resins. One effort involved the use of across-linking agent, as disclosed, for example, in U.S. Pat. Nos.4,604,434, 4,636,559, 4,701,538, and 4,767,840. This technique is ofteneffective, but difficulties are sometimes encountered by reason ofswelling of the cross-linked polycarbonate in the presence of organicliquids, and loss of ductility with increasing levels of cross-linkingagents.

Another limitation of certain BPA-polycarbonates is flame resistance.Although polycarbonate resins will normally merit the rating of"self-extinguishing" according to ASTM Method D 635, they will oftenreceive poorer ratings under UL-94 testing procedures.

Thus, there continues to be a need for BPA-polycarbonates that haveincreased solvent and flame resistance in combination with conventionalprocessability.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing and other limitations byproviding polymeric compositions resultant from blending a mixturecomprising: (A) at least one amorphous polycarbonate; (B) at least onecyclic polycarbonate oligomer containing hydroquinone carbonatestructural units; and (C) at least one polycarbonate formation catalyst.The present invention is based on the discovery that the solvent andflammability resistance of an amorphous polycarbonate are increased byblending therewith an effective amount of a cyclic polycarbonateoligomer containing hydroquinone structural units in the presence of apolycarbonate formation catalyst.

Accordingly, the present invention provides a method for increasing thesolvent and flame resistance of amorphous polycarbonates. Also providedis a novel class of solvent and flame resistant polycarbonate polymericcompositions. The polymeric compositions have particular application inthe preparation of shaped articles for use in environments characterizedby the presence of solvents, solvent vapors, and/or potential for openflames.

DETAILED DESCRIPTION

In one of its aspects, the present invention is directed to polymercompositions resultant from melt blending a mixture comprising:

(A) at least about 75 percent by weight of at least one amorphouspolycarbonate;

(B) up to about 25 percent by weight of a mixture comprising:

(1) at least about 50 percent by weight of at least one cyclicpolycarbonate oligomer;

(2) up to about 50 percent by weight of at least one linearpolycarbonate oligomer;

said linear and cyclic oligomers comprising carbonate structural unitsof the following formulae (I) and (II): ##STR1## wherein in formula (II)A¹ is a divalent group represented by the following formulae (III) or(IV): ##STR2## wherein in formula (III) each of R¹ and R² independentlyis a linear or branched alkyl group, and in formulae (III) and (IV) eachR³, R⁴, R⁵ and R⁶ independently is a linear or branched alkyl group, oris a halogen atom, and m and n independently are 0-4 and o and pindependently are 0-3; and wherein at least about 30 mole percent of thecarbonate structural units in said oligomers have formula (I); and

(C) at least about 0.01 mole percent based on the moles of carbonatestructural units in the mixture of a polycarbonate formation catalyst.

It is not certain whether any or all of the components (A), (B), and (C)used to prepare the polymeric compositions of the present inventioninteract chemically upon blending. Therefore, the present inventioncontemplates compositions comprising said components and any reactionproducts thereof, as well as optional components as describedhereinafter.

1. Amorphous Polycarbonate Resins

The term "amorphous" when used in conjunction with the polycarbonateresins of component (A) is intended to describe polycarbonates that aresubstantially devoid of crystallinity or stratification at processingtemperatures up to about 180° C. Such materials may possess some order,but it is insufficiently developed to result in loss of transparency orto be observed in routine x-ray crystallography spectra. Suchpolycarbonates, however, may become crystallized to some degree byprolonged heating at elevated temperatures or by exposure to solventssuch as acetone, as by immersion.

The amorphous polycarbonates (A) are available commercially and can alsobe prepared by several methods known in the art including those setforth in W. Christopher, et al., Polycarbonates, Reinhold PublishingCorporation, New York (1962). For example, they may be produced by theSchotten-Baumann reaction of phosgene with a diol in the presence of anappropriate hydrogen chloride acceptor or by a melt transesterificationreaction between the diol and a carbonate ester. In the former, phosgenereacts directly with the diol to produce a polymer in a solution. Thereaction may be run by employing an acid acceptor such as pyridine ortriethylamine, either in solution in a solvent such as methylenechloride or interfacially in a mixture of such a solvent and water. Thepolymer may be recovered as a solution after aqueous washes to removethe acid acceptor which has been neutralized or is present in excess. Intransesterification, a diphenyl carbonate reacts with the selected diolto give a phenol and a molten solvent-free polymer.

A number of diols including aliphatic, cycloaliphatic and aromaticdihydroxy compounds may be used in the above processes. Suitablearomatic dihydroxy compounds include, for example, thebis(monohydroxyaryl)alkanes and the bis(monohydroxyaryl) sulphones suchas:

2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane

2,2-bis-(4-hydroxyphenyl)propane (bisphenol A)

2,2-bis-(4-hydroxyphenyl)pentane

2,4'-dihydroxydiphenylmethane

bis-(2-hydroxyphenyl)methane

bis-(4-hydroxyphenyl)methane

bis-(4-hydroxy-5-nitrophenyl)methane

1,1-bis(4-hydroxyphenyl)ethane

3,3-bis(4-hydroxyphenyl)pentane

2,2-dihydroxybiphenyl

2,6-dihydroxynaphthalene

bis-(4-hydroxydiphenyl) sulfone

bis-(3,5-diethyl-4-hydroxyphenyl) sulfone

2,2-bis-(3,5-dimethyl-4-hydroxyphenyl)propane

2,4'-dihydroxydiphenyl sulfone

5'-chloro-2,4'-dihydroxydiphenyl) sulfone

bis-(4-hydroxydiphenyl)sulfone

4,4'-dihydroxydiphenyl ether

4,4'dihydroxy-3,3'-dichlorodiphenyl ether

4,4'dihydroxy-2,5-dihydroxydiphenyl ether

2,2-bis-(3,5-dibromo-4-hydroxyphenyl)propane.

Suitable aliphatic diols include for example, ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol,1,3-propanediol, 1,3-butanediol, 1,4-butanediol,2-methyl-1,3-propanediol, 1,5-pentanediol, 2-ethyl-1,3-propanediol,1,6-hexanediol, 1,8-octanediol, 1-ethyl-1,3-hexanediol, 1,10-decanediol,and the like.

Suitable cycloaliphatic dihydroxy compounds include, for example,1,4-cyclohexanediol, 1,2-cyclohexanediol,2,2-(4,4'-dihydroxy-dicyclohexylene)-propane, 2,6-dihydroxydecahydronaphthalene, the corresponding bis-alkoxylated aromaticdihydroxy compounds thereof, and the like.

For the purposes of the invention, it is also possible to utilizepolycarbonates (A) prepared by copolymerization of two or more of theabove diols or terpolymerization of the above diols. Amorphouscopolyester carbonates such as those disclosed in U.S. Pat. Nos.4,238,597 and 4,506,065, as well as amorphous branched polycarbonatessuch as those disclosed in U.S. Pat. No. 3,544,514 may also be used ascomponent (A) of this invention.

In one embodiment the amorphous polycarbonate (A) consists essentiallyof carbonate structural units of the following formula (V): ##STR3##wherein each of R⁷ and R⁸ independently is a linear or branched alkylgroup, each R⁹ and R¹⁰ independently is a linear or branched alkylgroup, or is a halogen atom, and x and y independently are 0-4.

For example, such structural carbonate units may be derived frombisphenol monomers including bisphenol A, 3,3',5,5'-tetrabromobisphenolA, 3,3',5,5'-tetrachlorobisphenol A and 3,3',5,5'-tetramethylbisphenolA.

The weight average molecular weight of the amorphous polycarbonates (A)is generally within the range of about 20,000 to about 80,000. Usually,the polycarbonates (A) will have a weight average molecular weightwithin the range of about 40,000 to about 60,000 (as determined by gelpermeation chromatography relative to polystyrene). In addition, it ispreferred in one embodiment that the polycarbonates (A) arehomopolymers. For example, homopolymeric BPA-polycarbonates such as GE'sLexan® polycarbonates having a number average molecular weight (relativeto polystyrene) of about 20,000 to about 30,000 are particularlypreferred.

2. Polycarbonate Oligomers

The polymeric compositions of the present invention are prepared byincorporating up to about 25 percent by weight of at least onepolycarbonate oligomer (B) containing carbonate structural units of theformulae (I) and (II). At least about 50 percent by weight of oligomers(B) have an overall cyclic structure, apart from the carbocyclic ringspresent in formulae (I)-(IV). The mixture may also contain up to about50 percent by weight of linear oligomers. In one embodiment, the mixturecontains from about 30 up to about 50 percent by weight of linearoligomers. In another embodiment the mixture is free of linearoligomers. The mixture includes oligomers having degrees ofpolymerization (i.e., average number of monomer units per oligomermolecule) from 3 to about 30 and preferably to about 20, with a majorproportion being up to about 12 and a still larger proportion up toabout 15. Mixtures of oligomers having varying degrees of polymerizationare preferred. Oligomers (linear or cyclic) having degrees ofpolymerization greater than about 30 are referred to herein as "highpolymer" and are generally not preferred. The cyclic oligomer mixturesof the invention are generally liquid at temperatures above 300° C. andmost often at temperatures above 225° C.

An essential feature of the oligomers (B) is the presence ofhydroquinone ("HQ") carbonate structural units (i.e., units of formula(I)) in amounts of at least about 30 mole percent. Hydroquinonecarbonate levels of at least about 50 mole percent are preferred. Mostoften, the oligomer mixture (B) contains hydroquinone units in amountsof about 55 mole percent. ##STR4##

Also present in the oligomers (B) of this invention are carbonate unitsof formula (II). In that formula, A¹ may be a divalent bisphenol groupof formula (III), in which each of R¹ and R² is an alkyl group asdefined. Most often, both R¹ and R² are methyl.

The R³ and R⁴ groups may be alkyl or halo as defined, and may be presentin quantities up to 4 per aromatic ring. The value of n is usually 0 or2, and each R³ or R⁴ group (when present) is usually methyl or bromo.Thus, the divalent groups of formula (III) are derived from bisphenolsknown in the art, especially bisphenol A or2,2-bis(4-hydroxyphenyl)propane. ##STR5##

The divalent A¹ groups may also have formula (IV); i.e., they may bederived from spirobiindane bisphenols which may contain R⁵ and R⁶substituents as previously defined, up to 3 such substituents beingpresent per aromatic ring. The preferred spirobiindane bisphenol is theunsubstituted 6,6'-dihydroxy-3,3,3'3'-tetramethylspiro(bis)indane.

The oligomers (B) may be prepared by contacting: (i) a mixture ofhydroquinone bischloroformates and bischloroformates of adihydroxyaromatic compound of the formula HO-A¹ -OH (wherein A¹ is asdefined above) with, (ii) at least one oleophilic aliphatic orheterocyclic tertiary amine, (iii) an aqueous base comprising an alkalior alkaline earth metal hydroxide or carbonate solution, and (iv) asubstantially non-polar organic liquid which forms a two-phase systemwith water. The bischloroformates are preferably maintained in lowconcentrations wherein the molar ratio of said amine to saidbischloroformates being about 0.06-2.0:1 and the molar ratio of saidbase to said bischloroformates being at least about 2.4:1. The oligomersobtained by this process are usually a mixture of both cyclic and linearoligomers often referred to as "crude cyclics". For a more detaileddescription of the preparation and isolation of cyclic polycarbonateoligomers, reference is made to U.S. Pat. No. 4,644,053 (Brunelle etal.) which is incorporated by reference herein.

(i) Bischloroformates

The bischloroformate mixture employed in the preparation of the crudecyclics may be a mixture of substantially pure monomeric hydroquinoneand bisphenol bischloroformates, which may be prepared, for example, bythe reaction of the corresponding dihydroxyaromatic compound withphosgene in the presence of a dialkylaniline, as disclosed in BritishPatent 613,280, the disclosure of which is incorporated by referenceherein.

For larger scale reactions, it is usually preferred for the sake ofeconomy to employ crude bischloroformate mixtures which may containoligomeric carbonate bischloroformates, a majority of said oligomericmaterials having degrees of polymerization up to about 5. Numerousmethods for preparing such crude bischloroformates are known; suitablemethods are disclosed, for example, in the following U.S. Pat. Nos.:

    ______________________________________                                                     3,255,230                                                                     3,312,661                                                                     3,966,785                                                                     3,974,126                                                                     4,638,077                                                        ______________________________________                                    

The disclosures of these patents are also incorporated by referenceherein.

A preferred method for preparing bischloroformate compositions useful inthe preparation of crude cyclics is disclosed in copending, commonlyowned application Ser. No. 07/299,572. It comprises passing phosgeneinto a mixture of water, a substantially inert, water-immiscible organicliquid, an alkali metal hydroxide, and hydroquinone or a mixture ofhydroquinone and bisphenol A containing at least about 40 mole percenthydroquinone; the ratio of moles of water to gram-atoms of alkalineearth metal hydroxide in said mixture being in the range of about5.0-5.5:1.

(ii) Tertiary amines

The tertiary amines employed in the preparation of the crude cyclics("tertiary" in this context denoting the absence of N--H bonds)generally comprise those which are oleophilic (i.e., which are solublein and highly active in organic media, especially those used in theoligomer preparation method), and more particularly those which areuseful for the formation of polycarbonates. Reference is made, forexample, to the tertiary amines disclosed in U.S. Pat. Nos. 4,217,438and 4,368,315, the disclosure of which are also incorporated byreference herein. They include aliphatic amines such as triethylamine,tri-n-propylamine, diethyl-n-propylamine and tri-n-butylamine and highlynucleophilic heterocyclic amines such as 4-dimethylaminopyridine (which,for the purposes of this invention, contains only one active aminegroup). The preferred amines are those which dissolve preferentially inthe organic phase of the reaction system; that is, for which theorganic-aqueous partition coefficient is greater than 1. This is truebecause intimate contact between the amine and the bischloroformates isessential for the formation of the crude cyclic mixture. For the mostpart, such amines contain at least about 6 and preferably about 6-14carbon atoms.

The most useful amines are trialkylamines containing no branching on thecarbon atoms in the 1- and 2-positions. Especially preferred aretri-n-alkylamines in which the alkyl groups contain up to about 4 carbonatoms. Triethylamine is often preferred by reason of its particularavailability, low cost, and effectiveness in the preparation of productscontaining low percentages of linear oligomers and high polymers.

(iii) Aqueous base

Also employed in the preparation of the crude cyclics mixture is anaqueous alkali or alkaline earth metal hydroxide or carbonate solution(hereinafter sometimes "aqueous base"), such as lithium, sodium,potassium or calcium hydroxide or sodium or potassium carbonate. It ismost often lithium, sodium or potassium hydroxide, with sodium hydroxidebeing preferred because of its availability and relatively low cost. Theconcentration of the solution is not critical and may be about 0.2-16 M.

(iv) Non-polar solvent

The fourth essential component in the preparation of crude cyclics is asubstantially non-polar organic liquid which forms a two-phase systemwith water. The identity of the liquid is not critical, provided itpossesses the stated properties. Illustrative liquids are aromatichydrocarbons such as toluene and xylene; substituted aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene and nitrobenzene;chlorinated aliphatic hydrocarbons such as chloroform and methylenechloride; and mixtures of the foregoing with ethers such astetrahydrofuran. Methylene chloride is generally preferred.

To prepare the crude cyclic oligomer mixture (B) according to theabove-described method, the reagents are brought into contact underconditions whereby bischloroformates are maintained at lowconcentration, generally up to about 0.5 M. Actual high dilutionconditions, requiring a large proportion of organic liquid, may beemployed but are usually not preferred for cost and convenience reasons.Instead, simulated high dilution conditions known to those skilled inthe art may be employed. For example, in one embodiment of the methodthe bischloroformates, and optionally other reagents, are addedgradually to a reaction vessel containing the organic liquid.

Although addition of bischloroformates neat (i.e., without solvents) iswithin the scope of this embodiment, it is frequently inconvenientbecause many bischloroformates are solids. Therefore, they arepreferably added as a solution in a proportion of the organic liquid.The proportion of organic liquid used for this purpose is not critical;about 25-75% (by weight) of the total, and especially about 40-60%, ispreferred. The reaction temperature is generally in the range of about0°-50° C. It is most often about 0°-40° C. and preferably 20°-40° C.

For maximization of the yield and purity of cyclic oligomers as opposedto linear oligomers, it is preferred to use not more than about 1.5 moleof bischloroformates per liter of organic liquid in the reaction system,including any liquid used to dissolve said bischloroformates.Preferably, about 0.003-1.0 mole of total bischloroformates is presentper liter of organic liquid. It should be noted that this is not a molarconcentration in said liquid when the bischloroformates are addedgradually, since they are consumed as added to the reaction system.

The molar proportions of the reagents constitute another importantfeature for yield and purity maximization. The preferred molar ratio ofamine to bischloroformates is usually about 0.06-2.0:1 and preferablyabout 0.1-0.25:1. That of base to bischloroformates is at least about1.4:1 and preferably about 2.5-3.1:1. In general, lower proportions ofbase (typically a molar ratio of about 1.4-2.0:1) are employed with acrude bischloroformate composition than with substantially pure monomerbischloroformates (about 2.75-3.1:1).

A factor of some importance is the concentration of available amine,which should be maintained at a level as constant as possible during theentire bischloroformate addition period. If all amine is present in thereaction vessel into which bischloroformates are introduced, itsconcentration steadily decreases, principally by dilution. On the otherhand, if amine is introduced continuously or in equal increments duringbischloroformate introduction, its available concentration is initiallylow and increases more or less steadily during the addition period.These fluctuations can result in a high and constantly varyingproportion of high polymer in the product.

It has been found advantageous to introduce the amine in one initiallarge portion, usually about 40-95% and preferably about 40-75% byweight of the total amount, followed by incremental or continuousaddition of the balance thereof. By this procedure, the concentration ofavailable amine is maintained at a fairly constant level in the organicphase during the entire addition period, and it is possible to minimizethe proportion of high polymer in the product.

Under these conditions, it is usually advantageous for the reactionvessel to initially contain about 5-40% and preferably about 5-30% oftotal aqueous base. The balance thereof is also introduced continuouslyor incrementally. As in the embodiment previously described, anotherportion of organic liquid may serve as a solvent for thebischloroformates.

Among the other principal advantages of this preferred embodiment arethe non-criticality of the degree of dilution of the reagents and theability to complete the addition and reaction in a relatively shorttime, regardless of reaction scale. It ordinarily takes a relativelyshort time to complete cyclic oligomer preparation by this method, andthe cyclic oligomer yield may be 85-90% or more. By contrast, use of analternate embodiment may, depending on reaction scale, require a muchlonger addition period and the crude product may contain substantialproportions of linear by-products with molecular weights of about4,000-10,000.

In one embodiment, the pH of the reaction mixture is typically in therange of about 9-14 and preferably about 12. When bischloroformates (andoptionally amine) are added to all of the aqueous base, on the otherhand, the initial pH remains on the order of 14 during essentially theentire reaction period.

In one embodiment, the cyclic oligomers (B) are recovered byconventional operations such as combining the crude cyclic, as a solidor in solution, with a diluent which is a non-solvent for said linearoligomers (B). Illustrative non-solvents include ketones such as acetoneand methyl isobutyl ketone and esters such as methyl acetate and ethylacetate. Acetone is a particularly preferred non-solvent. Recovery ofthe cyclic oligomers (B) is normally effected by simply separating thesame from the diluent by known methods such as vacuum evaporation. Inanother embodiment, the crude cyclics are used directly in the blendingprocess of the present invention.

3. Polycarbonate Formation Catalysts

The polycarbonate formation catalysts which can be used in the method ofthis invention include various bases (both Bronsted and Lewis) and Lewisacids. In general, the amount of catalyst used is about 0.01-1.0 molepercent based on the number of moles of carbonate structural units inthe mixture of components. Basic catalysts are exemplified by lithiumphenate, lithium salts of hydroxy-terminated polycarbonates,lithium2,2,2-trifluoroethoxide, n-butyllithium and tetramethylammoniumhydroxide. Also useful are various weakly basic salts such as sodiumbenzoate, lithium stearate and sodium salts of unsubstituted andsubstituted phenylacetic acids.

A particularly useful class of Lewis bases is disclosed in U.S. Pat. No.4,605,731, the disclosure of which is incorporated by reference herein.It comprises numerous tetraarylborate salts, including lithiumtetraphenylborate, sodium tetraphenylborate, sodium bis(2,2'-bisphenylene)borate, potassium tetraphenylborate,tetramethylammonium tetraphenylborate, tetra-n-butylammoniumtetraphenylborate, tetramethylphosphoniumtetraphenylborate,tetra-n-butylphosphonium tetraphenylborate and tetraphenylphosphoniumtetraphenylborate. The preferred catalysts within this class are thetetra-n-alkylammonium and tetra-n-alkylphosphonium tetraphenylborates.Tetramethylammonium tetraphenylborate is particularly preferred becauseof its high activity, relatively low cost and ease of preparation fromtetramethylammonium hydroxide and an alkali metal tetraphenylborate. Inanother embodiment, tetra-n-butylammonium tetraphenylborate is employedin the practice of the present invention.

Representative Lewis acids useful as polycarbonate formation catalystsinclude dioctyltin oxide; triethanolaminetitanium isopropoxide;tetra(2-ethylhexyl) titanate; polyvalent metal chelates such asbisisopropoxytitanium bisacetylacetonate (commercially available underthe trade name "Tyzor AA"), the bisisopropoxyaluminum salt of ethylacetoacetate and various transition metal acetylacetonates; andunsubstituted and substituted phenylacetic acids.

4. Additives and/or Fillers

The polymeric compositions of the present invention may 5 contain one ormore additives and/or fillers of the types used in the polymer art. Suchmaterials may be included in the polymer blends of the present inventionto modify or to obtain desirable properties. Fillers such as glasspowder, quartz products, graphite, metal powders, powders of highmelting synthetic resins, natural fibers, glass fibers, metal fibers,and the like may generally be included in the polymer compositions inamounts up to about 25 percent by weight.

Typical additives may be employed for color, thermal, hydrolytic andultraviolet stabilization of the polycarbonate compositions of thepresent invention in amounts up to about 2 percent by weight. Otheradditives such as mold release agents, pigments, flame retardants andthe like may also be present.

5. Blending Techniques

The polymeric compositions of the present invention including theamorphous polycarbonate (A), the polycarbonate oligomers (B), andoptional additives can be prepared by melt blending in the presence of apolycarbonate formation catalyst using techniques well-known to thoseskilled in the art. A blending method which results in the formation ofan intimate blend of the components is required. Suitable proceduresinclude solution blending and melt blending. A particularly usefulprocedure is to intimately mix the polymers using conventional mixingequipment such as a mill, a Banbury mixer, a Brabender Torque Rheometer,a single or twin screw extruder, continuous mixers, kneaders, etc. Forexample, the components may be intimately mixed in the form of granulesand/or powder in a high shear mixer. One preferred process involves: (1)mixing powdered components (A), (B) and (C) at ambient temperature in amixer; (2) drying the mixed powder at about 115° C.; and (3) meltblending the mixed powder in an extruder, to obtain the polymericcompositions of the present invention. "Intimate" mixing means that themixture is prepared with sufficient mechanical shear and thermal energyto produce a dispersed phase which is finely divided and homogeneouslydispersed in the continuous or principal phase.

Thus, in another of its aspects the present invention relates to methodsfor increasing the solvent and flammability resistance of amorphouspolycarbonates which comprises melt blending at least one amorphouspolycarbonate (A), with an effective amount of at least one cyclicpolycarbonate oligomer (B), in optional mixture with one or more linearoligomers, in the presence of a polycarbonate formation catalyst (C). Aneffective amount of oligomer (B) is usually up to about 25 percent byweight. The polycarbonate formation catalyst (C) is generally employedin an amount of at least about 0.01 mole percent based on the number ofcarbonate structural units in the mixture of components. The polymerblends of the present invention are characterized as having improvedflame and solvent resistance. The polymeric compositions of the presentinvention are particularly resistant to ketonic solvents such asacetone, diacetone alcohol, diethyl ketone, diisobutyl ketone,1,2-diketones, 1,3-diketones, 1,4-diketones, ethyl n-butyl ketone,mesityl oxide, methyl n-amyl ketone, methyl ethyl ketone, methylisobutyl ketone, and the like. However, the polymeric compositions ofthe invention have not been found to have increased resistance togasoline.

The polymeric compositions of the present invention can be processedinto shaped articles by extrusion, coextrusion, thermoforming,blow-molding, injection-molding, compression-molding, calendaring,laminating, stamping, pultrusion, etc. In particular, shaped articlescan be prepared by injection molding the blended polymer compositions ofthe present invention.

EXAMPLES

Various features and aspects of the present invention are illustratedfurther in the examples that follow. While these examples are presentedto show one skilled in the art how to operate within the scope of thisinvention, the examples are not to serve as a limitation on the scope ofthe invention since such scope is only defined in the claims.

Unless otherwise indicated in the following examples and elsewhere inthe specification and claims, all percentages are by weight, alltemperatures are in degrees Centigrade and if not specified are ambienttemperature, and all pressures are at or near atmospheric.

1. Preparation of bischloroformates

EXAMPLE 1

A 30 liter reactor was charged with 12.5 liters of CH₂ Cl₂, 752.4 gramsof hydroquinone (6.84 moles) and 1176.5 grams of bisphenol A (5.16moles). Phosgene was added at the fastest possible rate such that 2500grams were delivered in close to one hour. The reaction contained noinitial water and the reactor was maintained with the best possiblestirring. During the phosgenation reaction, the stoichiometric amount ofsodium hydroxide (24 moles; 1920 grams of 50% NaOH) was addedsubsurface. Following completion of the NaOH and phosgene addition, thereaction was pH controlled at pH=3-5, for 1/2 hour. Following this halfhour, four liters of water were added, the pH was raised to 8 and thetemperature was maintained below 20° C., until no phosgene was detected.The organic layer was then washed with 1N HCl, and was used directly inthe preparation of crude cyclics. Derivatization and hplc analysisindicated that the yield of hydroquinone bischloroformate was 44%, withabout 20% dimeric bischloroformate present.

EXAMPLE 2

A 30 liter reactor was charged with 660 grams of hydroquinone (6 moles),136 grams of bisphenol A (6 moles), and 8.2 liters of CH₂ Cl₂. Thereactor was stirred while cooling to 10°-15° C. for about 10 minutes,then phosgene was admitted at a rate of 36 g/min for 67 minutes (24.0moles). Concomitant to the phosgenation, a methylene chloride slurryconsisting of 933 grams of calcium hydroxide (12.6 moles) and 1.3 litersof CH₂ Cl₂ was added. Water was also added continuously at a rate of 18ml/min (1.2 liters total). The reaction temperature was maintainedbetween 15° and 18° C. Following completion of the phosgenation, thereaction was stirred for 30 minutes, while purging with nitrogen. Atthat time, about 2.4 liters of water was added, and 50% NaOH was added,while maintaining the pH at 8, until phosgene could no longer bedetected in the reactor. Finally, the phases were separated, and theorganic phase was washed with 0.1M HCl. Derivatization and analysis ofthe reaction product indicated 68% of theoretical hydroquinonebischloroformate and 79% of theoretical bisphenol A bischloroformate.The mixture was used in the cyclization reaction without furtherpurification.

2. Preparation of crude cyclic carbonates

EXAMPLE 3

The bischloroformate solution (nominal concentration=0.6M) prepared inExample 1 (20 liters) was placed in a pressure vessel and weighed, sothat addition over 30 minutes with constant flow was achieved. Thereactor was charged with 20 liters of CH₂ Cl₂, 240 m of Et₃ N, and oneliter of water. The reactor was brought to reflux, while stirring, andat that point addition with base was started. After approximately 2% ofthe base was added, bischloroformate addition was started, and additioncontinued over 30 minutes. Concomitant to bischloroformate addition, anadditional portion of Et₃ N (240 ml) was added (over 30 minutes), and30% NaOH

was added to maintain the pH at 9.5-11 (normally 1.2 moles of base/literof bischloroformate solution is necessary). After the addition wascomplete, 5 liters of water were added, followed by 5 liters of 1.0MHCl. The phases were separated, and the organic phase was washedsequentially with 1N HCl, 0.1N HCl, and water (three water washes). Theproduct (crude HQ-BPA cyclics containing linear oligomeric material) wasisolated by pumping the CH₂ Cl₂ solution into boiling water, leaving anoff-white powder, which was removed by filtration and was dried.

3. Preparation of polymer blends

EXAMPLES 4-7

In a Henschel mixer were placed 750 g of a commercially availablebisphenol A polycarbonate ("BPA PC") resin (M_(n) =28,000 relative topolystyrene) and 250 g of a mixture of hydroquinone-BPA crude cycliccarbonate and tetra-n-butylammonium tetraphenylborate ("borate")(prepared from 1759g of crude hydroquinone-BPA cyclic carbonate fromExample 3--55 mole percent hydroquinone and 45 mole percent BPA--and5.07 g of borate, which corresponds to 0.1 mole percent based on thenumber of bisphenol repeat units in the crude cyclics). This correspondsto 0.03 mole percent borate based on the total number of carbonatestructural units in the 75% BPA PC formulation. This formulation wasthen blended for 30 seconds. Also prepared were formulations comprisedof 50% BPA polycarbonate resin and 25% BPA polycarbonate resin as wellas a control (100% BPA polycarbonate resin). These mixtures were thendried in an air circulating oven at 115° C. for several hours prior toextrusion, which was achieved either on a Haake or a Werner andPfleiderer, WP-28 twin screw extruder.

The formulation containing 75 weight percent BPA polycarbonate materialwas extruded on a Haake twin screw extruder using the temperatureprofile 170° F. (zone 1), 315° F. (zones 2 and 3 and the die head). Thescrew speed was 225 rpm, the torque ranged from 10-60 percent. Thematerial was manually poked to aid feeding due to the tendency to"bridge".

The formulations comprised of 50% BPA polycarbonate resin and 25% BPApolycarbonate resin as well as a control (100% BPA polycarbonate resin)(blended as described above) were extruded on the WP-28 using thetemperature profile 326°-352° F. (zone 1), 574°-596° F. (zone 2),613°-629° F. (zone 3), 574°-576° F. (zone 4), 564°-583° F, and 582°-588°F. (die head). The materials were fed at a rate of about 80 g/minutewith a torque of from 64 to 76 percent and a screw speed set at themaximum.

4. Evaluation of Blends

EXAMPLES 8-11

The extrudates of Examples 4-7 were dried in an air circulating oven at250° F. overnight and injection molded on an 85 ton Van Dorn moldingmachine using the following conditions:--the mold temperature was 180°F.; the extruder barrel set temperature was 570° F.; the injectionpressure was 400 psi, while the back pressure was about 100 psi. Thetest parts molded were 0.125 inch Izod bars, flame bars, and tensilebars.

Evaluation of the materials for resistance to acetone was accomplishedby clamping a 21/2" long Izod test bar to a curved stainless steelstress jig (61/4" radius, which imposed a 1 percent applied strain onthe bar). This assembly was then immersed in a jar of acetone for 10minutes. The test was carried out three times for each extrudatematerial. The materials were also evaluated for notched Izod impactstrength, and melt viscosity. Table 1 summarizes the pertinent results.

                  TABLE 1                                                         ______________________________________                                        Evaluation of Blends of BPA Polycarbonate                                     and Crude Cyclic Oligomeric HQ-BPA Carbonates                                       Wt %     Mole %                                                         Ex.   BPA PC   Borate.sup.1                                                                            NI.sup.2                                                                           Behavior in Acetone                             ______________________________________                                         8    75       0.1       16.9 all bars remained in tact,                                                    some craze formation and                                                      chalking                                         9    50       0.1        0.7 all bars remained in tact,                                                    some craze formation                            10    25       0.1        0.3 all bars remained in tact,                                                    no craze formation                              11    100      --        16.9 instantaneously cracked                         ______________________________________                                         .sup.1 based on the number of bisphenol repeat units in the crude cyclics     .sup.2 notched Izod (ftlbs/inch of notch) ASTM D 256                     

EXAMPLES 12-15

The test bars molded in Examples 8-11 were evaluated for flammabilityresistance. Table 2 summarizes the pertinent results.

                  TABLE 2                                                         ______________________________________                                        Flame Resistance Evaluation                                                   of Various Materials                                                               Wt %                                                                     Ex.  BPA POLYCARBONATE Mole % Borate.sup.1                                                                        UL-94                                     ______________________________________                                        12   25                0.1          V-O                                       13   50                0.1          not tested                                14   75                0.1          V-O.sup.b                                 15   100               --           failed.sup.a                              ______________________________________                                         .sup.1 based on the number of bisphenol repeat units in the crude cyclics     .sup.a flaming drips on first ignition (1 bar) or second ignition (4 bars     .sup.b only 2 bars were available for testing                            

Although the above examples are limited to only a few of the variablesapplicable to the compositions and methods within the scope of thepresent invention, it should be understood that the scope of the presentinvention can be further appreciated by the description preceding theseexamples. Therefore, it is to be understood that the invention disclosedherein is intended to cover such modifications as fall within the scopeof the appended claims.

What is claimed is:
 1. A mixture comprising:(A) at least about 75percent by weight of at least one amorphous linear polycarbonate havinga weight average molecular weight, as determined by gel permeationchromatography, in the range of about 20,000-80,000; (B) at least onecyclic polycarbonate oligomer containing hydroquinone carbonatestructural units; and (C) at least one catalyst for conversion of cyclicpolycarbonates to linear polycarbonates.
 2. A mixture comprising:(A) atleast about 75 percent by weight of at least one amorphous linearpolycarbonate having a weight average molecular weight, as determined bygel permeation chromatography, in the range of about 20,000-80,000; (B)an amount up to about 25 percent by weight effective to increase thesolvent resistance of the amorphous linear polycarbonate of a mixturecomprising:(1) at least about 50 percent by weight of at least onecyclic polycarbonate oligomer; (2) up to about 50 percent by weight ofat least one linear polycarbonate oligomer; said linear and cyclicoligomers comprising carbonate structural units of the followingformulae (I) and (II): ##STR6## wherein in formula (II) A¹ is a divalentgroup represented by the following formulae (III) or (IV): ##STR7##wherein in formula (III) each of R¹ and R² independently is a linear orbranched alkyl group, and in formulae (III) and (IV) each R³, R⁴, R⁵ andR⁶ independently is a linear or branched alkyl group, or is a halogenatom, m and n independently are 0-4 and o and p independently are 0-3;and wherein at least about 30 mole percent of the carbonate structuralunits in said oligomers have formula (I); and (C) at least about 0.01mole percent based on the moles of carbonate units in the mixture of atleast one catalyst for conversion of cyclic polycarbonates to linearpolycarbonates.
 3. A composition according to claim 2 wherein component(B) contains at least about 50 mole percent of units of formula (I). 4.A composition according to claim 3 wherein component (B) contains about55 mole percent of units of formula (I).
 5. A composition according toclaim 2 wherein component (A) comprises homopolycarbonates,copolycarbonates, or copolyestercarbonates.
 6. A composition accordingto claim 5 wherein component (A) comprises bisphenol A polycarbonates.7. A composition according to claim 2 wherein A¹ has formula (III).
 8. Acomposition according to claim 7 wherein m and n are
 0. 9. A compositionaccording to claim 8 wherein R¹ and R² are methyl.
 10. A compositionaccording to claim 2 wherein A¹ has formula (IV).
 11. A compositionaccording to claim 9 wherein o and p are
 0. 12. A composition accordingto claim 2 wherein component (C) comprises a tetra-n-alkylammonium or atetra-n-alkylphosphonium tetraphenylborate.
 13. A composition accordingto claim 11 wherein component (C) comprises about 0.1 mole percent oftetrabutylammonium tetraphenylborate or tetramethylammoniumtetraphenylborate.
 14. A composition according to claim 11 whereincomponent (C) comprises about 0.03 mole percent of tetra-n-butylammoniumtetraphenylborate.
 15. A composition according to claim 2 whereincomponent (A) comprises at least about 75 percent by weight of at leastone amorphous polycarbonate consisting essentially of structural unitsof the following formula (V): ##STR8## wherein each of R⁷ and R⁸independently is a linear or branched alkyl group, each R⁹ and R¹⁰independently is a linear or branched alkyl group, or is a halogen atom,and x and y independently are 0-4.
 16. A composition according to claim2 wherein component (B) comprises from about 30 to about 50 percent byweight of linear oligomers.
 17. A mixture comprising:(A) at least about75 percent by weight of at least one amorphous linear polycarbonatehaving a weight average molecular weight, as determined by gelpermeation chromatography, in the range of about 20,000-80,000 andconsisting essentially of structural units of the following formula (V):##STR9## wherein each of R⁷ and R⁸ independently is a linear or branchedalkyl group, each R⁹ and R¹⁰ independently is a linear or branched alkylgroup, or is a halogen atom, and x and y independently are 0-4; (B) anamount up to about 25 percent by weight effective to increase thesolvent resistance of the amorphous linear polycarbonate of a mixtureconsisting essentially of(1) at least about 50 percent by weight of atleast one cyclic polycarbonate oligomer; (2) up to about 50 percent byweight of at least one linear polycarbonate oligomer; said linear andcyclic oligomers consisting essentially of carbonate structural units ofthe following formulae (I) and (II): ##STR10## wherein in formula (II)A¹ is a divalent group represented by the following formula (III):##STR11## wherein in formula (III) each of R¹ and R² independently is alinear or branched alkyl group, each R³ and R⁴ independently is a linearor branched alkyl group, or is a halogen atom, and m and n independentlyare 0-4; and wherein at least about 55 mole percent of the structuralunits in said oligomers have formula (I); and (C) at least about 0.1mole percent based on the moles of carbonate units in the mixture of acatalyst for conversion of cyclic polycarbonates to linearpolycarbonates comprising a tetra-n-alkylammonium tetraphenylborate. 18.A composition according to claim 17 wherein component (C) comprisesabout 0.03 mole percent of tetra-n-butylammonium tetraphenylborate. 19.A method for increasing the solvent resistance of an amorphous linearpolycarbonate which comprises blending said amorphous linearpolycarbonate having a weight average molecular weight, as determined bygel permeation chromatography, in the range of about 20,000-80,000, inthe presence of a catalyst for conversion of cyclic polycarbonates tolinear polycarbonates and an effective amount of a mixturecomprising:(1) at least about 50 percent by weight of at least onecyclic polycarbonate oligomer; (2) up to about 50 percent by weight ofat least one linear polycarbonate oligomer; said linear and cyclicoligomers comprising structural units of the following formulae (I) and(II); ##STR12## wherein in formula (II) A¹ is a divalent grouprepresented by the following formulae (III) or (IV): ##STR13## whereinin formula (III) each of R¹ and R² independently is a linear or branchedalkyl group, and in formulae (III) and (IV) each R³, R⁴, R⁵ and R⁶independently is a linear or branched alkyl group, or is a halogen atom,m and n independently are 0-4 and o and p independently are 0-3; andwherein at least about 30 mole percent of the carbonate structural unitsin said oligomers have formula (I); and (C) at least about 0.01 molepercent based on the moles of carbonate units in the mixture of at leastone catalyst for conversion of cyclic polycarbonates to linearpolycarbonates.
 20. A method according to claim 19 wherein said solventcomprises acetone, diacetone alcohol, diethyl ketone, diisobutyl ketone,1,2-diketones, 1,3-diketones, 1,4-diketones, ethyl n-butyl ketone,mesityl oxide, methyl n-amyl ketone, methyl ethyl ketone, or methylisobutyl ketone.
 21. A method for increasing the flammability resistanceof an amorphous linear polycarbonate which comprises blending saidamorphous linear polycarbonate having a weight average molecular weight,as determined by gel permeation chromatography, in the range of about20,000-80,000 in the presence of a catalyst for conversion of cyclicpolycarbonates to linear polycarbonates and an effective amount of amixture comprising:(1) at least about 50 percent by weight of at leastone cyclic polycarbonate oligomer; (2) an amount up to about 50 percentby weight of at least one linear polycarbonate oligomer; said linear andcyclic oligomers comprising structural units of the following formulae(I) and (II): ##STR14## wherein in formula (II) A¹ is a divalent grouprepresented by the following formulae (III) or (IV): ##STR15## whereinin formula (III) each of R¹ and R² independently is a linear or branchedalkyl group, and in formulae (III) and (IV) each R³, R⁴, R⁵ and R⁶independently is a linear or branched alkyl group, or is a halogen atom,m and n independently are 0-4 and o and p independently are 0-3; andwherein at least about 30 mole percent of the carbonate structural unitsin said oligomers have formula (I); and (C) at least about 0.01 molepercent based on the moles of carbonate units in the mixture of at leastone catalyst for conversion of cyclic polycarbonates to linearpolycarbonates.